Isolating switch having spherical, ellipsoid, toroid or spheroid electrodes and a retractable switchblade

ABSTRACT

An isolating switch having spherical, ellipsoid, toroid or spheroid electrodes and a retractable switchblade. The electrodes in the open gap position have a relatively high withstand on switching voltage surge, impulse voltage and with a relatively small gap space. The extension of the retractable switchblade to contact both electrodes corresponds to the closed position of the switch while retraction of the switchblade into one of the electrodes corresponds to the open position. In that latter position, an open gap is produced between the electrodes and results in a substantially uniform electrostatic field in the gap. This has the advantage that the switch open gap may be made substantially shorter than the distance from the electrodes to ground and yet insure that any flashover will be between the electrodes and ground rather than across the switch open gap.

United States Patent [72] Inventor [2|] Appl. No. [22] Filed [45] Patented [73) Asslgnee Joseph A. Turgeon Toronto, Ontario. Canada July 7, I969 July 13, I971 I-T-E-Clreult Breaker (Canada) Llmlted Port Credit, Ontario, Canada [54] ISOLATING SWITCH HAVING SPHERICAL,

ELLIPSOID, TOROID OR SPHEROID ELECTRODES AND A RETRACTABLE 2,310,093 2/1943 Komdorfer 200/148 FOREIGN PATENTS 517,622 211940 GreutBrltaln....... ZOO/148 Primary Examiner-- Robert K. Sehaeter Assistant Examiner-H. J. Hohauser Attorney-Ostrolenk, Faber, Gerb and Sotfen ABSTRACT: An isolating switch having spherical, ellipsoid, toroid or spheroid electrodes and a retractable switchblade. The electrodes in the open gap position have a relatively high withstand on switching voltage surge, impulse voltage and with a relatively small gap space. The extension of the retractable switchblade to contact both electrodes corresponds to the closed position of the switch while retraction of the Switchblade into one of the electrodes corresponds to the open position. In that latter position, an open gap is produced between the electrodes and results in a substantially uniform electrostatic field in the gap. This has the advantage that the switch open gap may be made substantially shorter than the distance from the electrodes to ground and yet insure that any flashover will be between the electrodes and ground rather than across the switch open gap.

PATENTED JUL 1 3 I971 SHEET 2 BF 5 BACKGROUND OF THE INVENTION This invention relates to electrical switches, and to high voltage air isolating switches of the disconnect type. More specifically, it relates to such switches which are provided with a novel electrode arrangement which substantially minimizes the danger of flashover in the open gap when the switch is in its disconnect position, so as to substantially reduce the open gap dimension heretofore required.

Disconnecting switches are designed to isolate electrical apparatus and portions of electrical systems from energized lines for the safe handling, maintenance, repair and inspection they require. It is, therefore, of the utmost importance to provide adequate protection for personnel working in the immediate region of the disconnected equipment. Hence when the switch is open, it is necessary that the gap in the open position be adequate to withstand all usual, as well as unusual, voltages which are impressed upon it by the system. lf a surge voltage causes the switch open gap to flashover, the lives of personnel may be placed in serious jeopardy.

Such disconnecting switches are customarilydesigned so that the switch open gap will withstand higher voltages than the insulator columns which support the energized parts from the grounded metal base. As a result, flashover is much more likely to occur between the energized parts and ground, than across the switch open gap. In this manner, the insulator columns provide protection for the switch and operating personnel against switching surge voltages, and impulse voltages. However, this requires the provision of very large open gaps in the switch to insure greater insulation strength or withstand than exists across the insulator columns.

In the past, disconnecting switches have been constructed with large'open gaps with nonuniform electric field distribution because of the geometry of the switchblade and associated contacts. In some instances, methods were provided to reduce the insulation strength of the insulator columns to insure higher insulation strength across the open gap that existed down the insulator columns to earth. These methods have included the use of devices such as rod electrodes connected to the base of the insulator columns. These methods, however, have all suffered two critical drawbacks.

The first drawback is that the effective insulation strength or withstand of the insulator column cannot be reduced without limitation. The effective withstand of the column cannot be reduced, for example, to the point where it will not .be sufficient under high voltage conditions when the system is in operation. If the withstand of the insulator columnis too low, the system will not be able to function properly or reliably.

The second drawback is that the gap between the switchblades of the disconnecting switch in all ofthese cases establishes the insulating distances as essentially that between rod electrodes, i.e., behaves like a rod gap, and since the withstand of the insulator column must always be'sufficiently high, this gap must of necessity remain largc.'The necessity of this large gap distance further creates a situation subject to anomalous flashovers rather than the required controlled flashover to ground. With a very large gap behaving like a rod gap, it is very difficult to obtain the required flashover control.

In the same way that voltages of 500 and 700 kilovolts have been recently developed as overlay for 300-345 kilovolt systems, 1000-1500 kilovolts is presently being developed for future overlay on 500 and 700 kilovolt systems. The formidable factor in such system design has been to provide sufficiently high switching surge insulation strength. With the successful application of surge control in power circuit breakers and advances-in surge diverter design, switching surges can be limited to a sufficiently low level that operating voltages can be increased to 1000 1500 kilovolts with no greater probability of flashover than on the present 700 kilovolt systems.

These 700 kilovolt systems have a switching surge withstand of 1350 kilovolts, impulse withstand of 2100 kilovolts, power frequency withstand of 970 kilovolts, and with no visible corona at 500 kilovolts to ground. Future 1500 kilovolt systems may require a switching surge withstand of 2300 kilovolts, impulse withstand of 2600 kilovolts, power frequency withstand of 2000 kilovolts, and with no visible corona at 1300 kilovolts to ground.

In the near future transmission systems will be developed using voltages as high as 1000-1500 kilovolts. These systems require disconnecting switches having insulator columns with sufiicient voltage withstand. The insulator columns may be of the order of 20 feet to provide adequate withstand for switching surges of 2300 kilovolts or so. Under these conditions, the switch open gap using existing switchblade arrangements may be considerably longer (e.g. 25-30 feet) to insure that flashover will be down the insulator column rather than across the open gap. By means of the present invention, the switch open gap has been reduced to between 6 and 7 feet while minimizing the flashover across the open gap.

This invention provides a new and novel switch open gap whereby the switch open gap is substantially shortened to produce greater control of any flashovers without the necessity of reducing the effective withstand of the insulator columns. This invention also permits the use of shorter switchblades and a shorter mounting base to effect a substantial saving; and, especially in situations where the withstand of the insulator column is not required to be high under operating conditions, these components may be shortened even further.

This invention also permits a substantial savings in yard space as a result of the use of shorter switchblades and shorter switch open gaps.

This invention solves the problems of the prior art by providing new and novel switchblade electrode arrangements which set up a substantially uniform electrostatic field over a wide but controlled area when the electrodes are in their disconnect position rather than the concentrated electrostatic field previously established by switchblade and electrode arrangements producing rod type gaps. As will become apparent hereinafter, the present invention represents a modification of that invention disclosed in applicant's pending U.S. application Ser. No. 681,743, filed Nov. 9, 1967 as U.S. Pat. No. 3,493,699 on 3 Feb. 1970 entitled Isolating Switch with Sphere Gap" to J. A. Turgeon, and assigned to the same assignee as the instant invention.

In one embodiment of the invention, a disconnect switch is provided with a pair of spherical electrodes supported on insulator columns. A retractable switchblade is also provided and is arranged to slidably connect and disconnect the spherical electrodes. When the spherical electrodes are connected by the retractable switchblade, the disconnect switch is in its closed position. When the spherical electrodes are disconnected (resulting from the withdrawal of the retractable switchblade into one of the spherical electrodes, for example), the disconnect switch is in its open position, with the separation between the two spherical electrodes defining the switch open gap. With the retractable switchblade in this withdrawn position, a sphere gap is produced and any potential difference between the two spherical electrodes will set up a substantially uniform electrostatic field. Since the electrostatic field is substantially uniform and over a wide area, the voltage necessary to cause any flashover in the switch open gap will be far greater than is necessary for a rod gap having the same electrode separation and the switch open gap may be decreased substantially.

Accordingly, a primary object of the invention is to provide a novel switch opengap to protect against flashover in the gap in disconnect type switches.

Another object of the invention is to provide a novel construction for disconnecting switches whichpermits a decrease in the'length of the switch open gap of the switch.

A further object of the invention is to provide a novel switchblade and electrode arrangement having minimum blade length and still preventing open gap breakdown on the occurrence of surge voltages.

An additional object of the invention is to provide a disconnect switch, wherein the switch open gap is substantially shorter than the insulator column and yet insures against flashover in the switch open gap itself.

Yet another object of the present invention is to provide a disconnect switch having integrated coordinated switchblade and electrode arrangements, insulator columns and base ground to insure proper contact when the switch is closed and proper positioning of the electrodes when the switch is open.

These and other objects of the invention will become apparent from a reading of the accompanying description and drawings in which:

FIG. 1 is an elevational view of an embodiment of the disconnect switch of the instant invention with the switch in its closed position;

FIG. 2 is an elevational view of the disconnect switch of the invention with the switch in its open position;

FIGS. 3 and 4 are elevational views of another disconnect switch according to the invention, in its closed and open positions, respectively;

FIGS. 5 and 6 are similar views of a further disconnect switch constructed in accordance with the present invention; and

FIG. 7 illustrates the relative sizes of the'component parts of the disconnect switches ofthe invention.

DESCRIPTION AND OPERATION OF THE SWITCH OF FIGS. 1 AND 2 Referring now to FIGS. I and 2, there is shown a two-insulator disconnect switch assembly comprised of a supported switch base 10 which is preferably of a rigid metallic structure. The switch base 10 is electrically grounded by a suitable conductor (not shown). The switch base 10 is provided with means 13 which secure the lower portions of the insulator columns 14, in any desirable manner, such that the insulator columns 14 are stationary with respect to base 10.

The opposite ends of the insulator columns 14 cooperate to support a pair of metallic electrodes and a retractable switch blade constructed in accordance with the present invention. In particular, the insulator columns 14 rigidly support a pair of spherical electrodes 15, 16, each of which has an opening in that portion of its surface nearest to the other spherical electrode. In one construction of the invention, the spherical electrodes were constructed to be 6 feet 6 inches in diameter and spaced apart a distance of 7 feet.

Conductors I7 and 18 are respectively coupled to these spherical electrodes 15 and 16 in this and other environments, in any suitable manner, and connect these electrodes to suitable utilization apparatus (not shown); It is to be noted that while solid spherical electrodes have been shown, the electrodes 15 and 16 may also be toroidal shaped rings, ellipsoids or spheroids however providing spherical surfaces towards each other in the position of the airgap.

The retractable blade 19 for alternately closing and opening the disconnect switch is shown as being in alignment with the plane formed by the openings in the two spherical electrodes. This blade is operated to slide within the openings and to make electrical contact between the two spherical electrodes when the switch is desired to be closed. When the switch is to be opened, the. blade 19 is arranged to wholly retract within the spherical electrode 16. In that instance, the near surfaces of the spherical electrodes 15 and 16 will present the above described open gap of a nature which establishes a uniform electrostatic field. As was previously mentioned, a 7 foot gap between these spherical electrodes 15 and 16 will suffice to minimize the possibility of flashover whereas a rod type gap oftentimes requires a spacing of 27 feet and more to prevent against flashover for these ultrahigh, kilovolt voltages of comparable amount.

The retraction of the blade 19 within the spherical electrode 16-and conversely, its movement to connect to the spherical electrode 15 is controlled by the rotation of a gear 20 on a threaded portion 21 located within the spherical electrode 16. More particularly, the gear 20 is driven by a gear 22 through a conventional chain drive 23 by a rotating stack 25. In this respect, it will also be noted that the gear 22 and the chain drive 23 are also included within the confines of the spherical electrode 16. A motorized gear box 26 is shown as providing the rotational drive for the stack 25. Both these latter components, namely the stack 25 and the gear box 26, are located external to the electrode 16 but are held in secure relationship thereto.

The closing stroke of the retractable blade 19 effectively drives the blade 18 into the opening of the spherical electrode 15. At the end of the closing stroke directed by the gear box 26, the blade 19 is rotated by a cam 27 to fit within the contact fingers ofajaw 28 located within the latter electrode 15. It will be noted that whereas the cam 27 is positioned within the spherical electrode 16, the jaw 28 is located within the spherical electrode 15 and serves to obtain a high pressure contact when the disconnect switch is in its closed position.

If for some reason the switch must be disconnected, such as for maintenance, repair or inspection, the motorized gear box 26 operates the rotating stack 25, the chain drive 23, the gears 20 and 22 and the cam 27 in the direction to withdraw the retractable blade wholly within the confine of the spherical electrode 16. In this respect, it will be understood that the length of the retractable blade 19 is sufficient to make contact between the gears of the spherical electrode 16 and the jaw 28 of the electrode 15, while at the same time being short enough so as not to protrude beyond the surface of the electrode 16 when the blade is completely withdrawn. It will be seen that this can be effected when employing a retractable blade having a longitudinal dimension greater than the airgap distance but less than the diameter of the spherical electrode 16 measured along an axis substantially parallel to the direction of switchblade movement. I

It is, therefore, seen that complete withdrawal of the retractable arm 19 into the electrode 16 produces a gap condition which is entirely spherical in nature. This sphere gap produces a substantially uniform electrostatic field in the switch open gap, and requires a much higher voltage for flashover across the gap than that for a rod gap of the same spacing.

DESCRIPTION AND OPERATION OF THE SWITCH OF FIGS. 3 AND 4 Referring now to FIGS. 3 and 4, there is shown another twoinsulator disconnect switch assembly embodying the present invention. A motor mechanism there rotates an insulator shaft 101 which, in turn, rotates a-bevel gear 102. The bevel gear 102 is shown as being engaged to a second bevel gear 103 at point 104. The gear 103 is fixed to 'a threaded shaft 105, which is supported at one end by a bearing 106 and at the other end engages a threaded nut 107 fixed to a retractable switchblade 108. The switchblade 108 is, in turn, supported by a plurality of rollers 10?, and is prevented from turning on its longitudinal axis by a guide 110 along a track 111. The rotation of the insulator stack 101 under control of the motor 100 causes the switchblade 108 to extend or withdraw from the contacts 112 which are biased by garter springs 113.

The electrodes in this instance are generally spherical, but with a protuberance at opposite ends. Even with this modification, however, a substantially uniform sphere gap condition exists between the electrodes at the point where flashover is possible. As will be apparent, this protuberance just serves as a means of housing a retractable blade having a longitudinal dimension which not only is greater than the spacing between the electrodes (as was the case in FIGS. I and 2), but which is also greater than the diameter of the spherical electrode employed (as contradistinct from that of FIGS. 1 and 2).

Referring once again to FIGS. 3 and 4, the generally spherical electrode 120 is supported on the insulator stack 121, and is provided with sliding contacts 122 biased by a garter spring 123. An opening 124 is shown in the near surface of the spherical electrode 120 to allow the switchblade 108 to extend into the opening 125 of the other, generally spherical electrode 126. That electrode 126 is also supported on an insulator stack 127, so that the electrical connection between the electrodes 120 and 126 can be made or broken by simply rotating the insulator stack 101. In this respect, it will be seen that the longitudinal dimension of the switchblade 108 is greater than the spacing between the near surfaces of the electrodes 120 and 126, but, in this case, is greater than the diameter of that portion of the electrode 120 which is substantially spherical in nature. The added length in this instance extends into the protuberance to the left of the spherical electrode 120. I

As another illustration of a disconnect switch according to the invention, it will be appreciated that where large gaps are required as the operating kilovoltage increases, both of the electrodes 120 and 126, as in FIGS. 3 and 4, could be provided with movable blades to fill the length of the airgap spaces. The end of one blade can be fitted with a male contact and supported, for example, in electrode 120, while the end of the other blade, supported'in electrode 126, could be fitted with a female contact. The two contacts would then be engaged within the gap when corresponding drive mechanisms are employed with both blades to extend them from the electrodes to m ke the contact and to withdraw them into the electrodes when the contact is to be broken. Where the two blades are of equal lengths, the engagement would occur in the center of the airgap.

One advantage of the arrangement shown in FIGS. 3 and 4 (and in FIGS. 5 and 6 described below) results from the location of the insulator column behind the electrode surface, i.e., away from the open gap. This placement is for the purpose of insuring that the electrostatic field existing between adjacent faces of the electrodes 120 and 126 (220 and 226 in FIGS. 5 and 6) is in no way affected by the location of an insulator column. With this placement, electrostatic fields existing between the electrodes employed is substantially uniform, to further reduce the possibility of anomalous flashover.

DESCRIPTION AND OPERATION OF THE SWITCH OF FIGS. 5 AND 6 Referring now to FIGS. 5 and 6, there is shown a further two-insulator disconnect switch assembly embodying the principles of the present invention. As with the previous two embodiments of the invention, the first of these FIGS. (FIG. 5) shows the switch in its closed position, while the second of these FIGS. (FIG. 6) shows the switch in its open position.

In FIGS. 5 and 6, a motor mechanism 200 rotates an insulator shaft 201 which, in turn, rotates a bevel gear 202. This gear 202 is engaged to a second bevel gear 203 at a point 204. The gear 203 is fixed to a threaded shaft 205, which is supported at one end by a bearing 206 and at the other end is in engagement with a threaded nut 207 fixed to a retractable switchblade 208. The switchblade 208, as in FIGS. 3 and 4, has a fixed guide 209 provided at each end with a plurality of rollers 210. These rollers 210 travel along tracks 211 which are substantially straight between the points 1-1 and 2-2. These tracks 211 are further curved, as shown in detail in the insert of FIG. 5, one curved portion existing between the points 2-2 and 3-3, another between the points 3-3 and 4-4, and a third between the points 4-4 and 5-5. The rotation of the insulator stack 201 under control of the motor 200 causes the switchblade 208 to extend or withdraw from the contacts of the electrodes 220 and 226.

As the retractable switchblade 208 advances from the open position shown in FIG. 6 up to the point 6 (shown in the insert of FIG. 5), a pair of switchblade beaver tails" 212 and 213 are vertically disposed. As the blade 208 advances to points '7, 8 and 9, the blade 208 and the beaver tails" 212 and 213 are rotated due to the curved portions 3-3, 4-4 and 5-5 of the track 211. At the end of curbed portions 5-5, the blade 208 and beaver tails 212 and 213 have been rotated substantially to a horizontal position. In that position, the retractable switch blade 208 engages the two jaw contacts 214 and 215 to complete the electrical connection between the vertical electrodes 220 and 226.

The principal advantage of the retractable blade arrangement of FIGS. 5 and 6 is that the arrangement utilizes jaw contacts of proven design for icing conditions. If the switchblade is coated with ice due to its use in an external environment, the curved roller portion of the drawings serve to break the ice from the blade and to free the ice so that it would not interfere with the electrical contacts when the switch is to be closed. Also, it will be seen that if the ice has formed on the retractable switchblade 208 while the switch is closed, the curved portion of the tracks 211 will clear the ice from the switchblade when the switch is to be opened in response to direction from the motor mechanism 200.

The electrical advantage of all these sphere gap switches include better corona control, a more uniform flashover characteristic with less tendency to anomalous flashover, and a greater ease of gap coordination with insulation to ground. The large electrodes employed would further have a grading effect on the supporting insulators and a better voltage distribution to reduce the height of the insulator stack substantially.

In accordance with the present invention, adequate protection for personnel is provided against flashover in the switch open gap by this substantially uniform distribution of the electrostatic field in the gap region. The substantially uniform electrostatic field requires a much higher voltage for fiashover than does the concentrated electrostatic field of a rod gap. Furthermore, with the more uniform electrostatic field, the switch open gap may be considerably shortened (to, for example, the 7 foot of one arrangement of the invention) and can be more easily coordinated with the withstand characteristic of the insulator column. As an example of the great savings in space possible with the instant invention, it has been found that in a 1000 to 1500 kilovolt system requiring an insulator column length of over 20 feet, the use of spherical electrodes of a diameter of 6% feet permits the provision of a switch open gap of only the 7 feet described. Such relative dimensions are illustrated in FIG. 7 as applicable to the FIGS. 1 and 2 arrangements. It is seen that this switch open gap is considerably shorter than the insulator column and still provides adequate protection against fiashover in the gap.

It will therefore be seen that the instant invention provides an alternative solution to problems involving flashover than is described in applicant's aforementioned pending U.S. application Ser. No. 681,743. There, instead of using a retractable blade to connect and alternatively disconnect the electrodes employed, a pair of rotating switchblades were employed to place the switch in either one of an opened and closed position. Thus, although the invention disclosed in the Ser. No. 68 l ,743 application affords the desirable features and advantages set forth therein, the invention of the instant application offers many additional desirable features of its own. These additional features should not be construed, however, as detracting from the attractiveness of that invention, as there, too, the advantage of reducing the possibility of fiashover with decreased gap dimensions is also provided.

The principal advantages of this invention over air disconnect switches of previous design not only include its reduced physical size and its high withstand to overvoltages, but also include the fact that its operation is one free of corona and characterized by a relatively low radio interference voltage. Also, aside from the sphere gap having a more uniform field than a rod gap, it should be noted that the sphere gap as described herein does not distort the electrostatic field in the manner associated with the grounded, open blade rod gap. Thus, the retractable sphere gap arrangement of the instant invention eliminates the the need for previously employed gap grading posts, as well. These and other advantages will be well recognized and appreciated by those skilled in the art.

While the present invention has been described as using smooth, continuous, solid metallic electrodes, alternative arrangements could use electrodes made of wire mesh, expanded metal, or of a lattice structure. Such configurations are attractive in inclement weather situations as they aid in suppressing noise generation, will allow rain to pass through to avoid a cascading stream thus minimizing the upsetting of a uniform electrostat field, and are well suited to the retractable blade switching arrangements of FIGS. and 6.

The embodiments of the invention in which an exclusive privilege and property is claimed are defined as follows:

1. A high-voltage electric disconnect switch for ratings of 1,000 kv. and above comprising:

first and second fixed spaced-apart electrodes having only air therebetween and operative to produce a substantially uniform electrostatic field in the air between facing surfaces thereof when in a disengaged switch position, each such electrode having an opening in its respective facing surfaces;

a retractable switchblade; and

means operative to move said switchblade between said electrodes and through said surface openings to contact said electrodes when in an engaged switch position and to withdraw said retractable switchblade within at least one of said two electrodes to break said contact when in said disengaged position;

the longitudinal dimension of said switchblade being greater than the spacing between said electrode surfaces.

2. An electric switch as defined in claim 1 wherein said retractable switchblade is a two-piece unit, wherein each of said two pieces are withdrawn within said spaced-apart electrodes to break said contact when in said disengaged position, and wherein the longitudinal dimension of each such piece is less than the dimension of its respective electrode within which said piece is withdrawn, said electrode dimension being measured along an axis substantially parallel to the plane of said switchblade movement.

3. An electric switch as defined in claim 1 wherein said first and second electrodes comprise a pair of spherical electrodes spaced apart by a distance approximately equal to their diameter and operative to produce a substantially uniform electrostatic field in the air therebetween when in a disengaged switch position.

4. An electric switch as defined in claim 3 wherein said first and second spherical electrodes are mounted on first and second insulator columns, respectively, said insulator columns being more than three times longer than the diameter either of said first or second electrodes, and wherein said insulator columns are supported by an electrically grounded base.

5. An electric switch as defined in claim 4 wherein the distance between said spherical electrodes when the switch is in its disengaged position is substantially shorter than the length of said insulator columns and the breakdown voltage for flashover is greater between said first and second electrodes than it is from said electrodes to said grounded base across the respective insulator column lengths.

6. A high-voltage disconnect switch for ratings of 1,000 kv. and above comprising:

first and second fixed spaced-apart electrodes having air only therebetween operative to produce a substantially uniform electrostatic field in air between facing surfaces thereof when in a disengaged switch position, each such electrode having an opening in its respective facing surface; and a retractable switchblade arranged to slidably move within at least one of said two electrodes in a direction alternatively towards and away from said other electrode by drive means positioned within at least said one electrode to connect and disconnect said electrodes, respectively, by contact means positioned within said other electrode; the longitudinal dimension of said retractable switchblade being reater than the spacing between said electrodes. 7. A hig -voltage electric disconnect switch for ratings of 1,000 kv. and above comprising:

first and second fixed spaced-apart electrodes having only air therebetween operative to produce a substantially uniform electrostatic field in the air between facing surfaces thereof when in a disengaged switch position, each such electrode having an opening in its respective facing surface;

a retractable switchblade; and

means operative to move said switchblade between said electrodes and through said surface openings to contact said electrodes when in an engaged switch position and to withdraw said retractable switchblade within one of said two electrodes to break said contact when in said disengaged position;

the longitudinal dimension of said switchblade being greater than the spacing between said electrode surfaces but less then the dimension of said one of said spaced-apart electrodes within which said switchblade is withdrawn, said electrode dimension being measured along an axis which is substantially parallel to the plane of switchblade movement.

8. An electric switch as defined in claim 7 wherein said first and second spaced-apart electrodes are operative to produce a sphere gap condition therebetween when in said disengaged switch position.

9. An electric switch as defined in claim 8 wherein said spaced-apart electrodes comprise a pair of spherical electrodes and wherein the longitudinal dimension of said switchblade is greater than the spacing between the facing surfaces of said spherical electrodes but less then the diameter of that one of said spherical electrodes within which said switchblade is withdrawn. 

1. A high-voltage electric disconnect switch for ratings of 1,000 kv. and above comprising: first and second fixed spaced-apart electrodes having only air therebetween and operative to produce a substantially uniform electrostatic field in the air between facing surfaces thereof when in a disengaged switch position, each such electrode having an opening in its respective facing surfaces; a retractable switchblade; and means operative to move said switchblade between said electrodes and through said surface openings to contact said elecTrodes when in an engaged switch position and to withdraw said retractable switchblade within at least one of said two electrodes to break said contact when in said disengaged position; the longitudinal dimension of said switchblade being greater than the spacing between said electrode surfaces.
 2. An electric switch as defined in claim 1 wherein said retractable switchblade is a two-piece unit, wherein each of said two pieces are withdrawn within said spaced-apart electrodes to break said contact when in said disengaged position, and wherein the longitudinal dimension of each such piece is less than the dimension of its respective electrode within which said piece is withdrawn, said electrode dimension being measured along an axis substantially parallel to the plane of said switchblade movement.
 3. An electric switch as defined in claim 1 wherein said first and second electrodes comprise a pair of spherical electrodes spaced apart by a distance approximately equal to their diameter and operative to produce a substantially uniform electrostatic field in the air therebetween when in a disengaged switch position.
 4. An electric switch as defined in claim 3 wherein said first and second spherical electrodes are mounted on first and second insulator columns, respectively, said insulator columns being more than three times longer than the diameter either of said first or second electrodes, and wherein said insulator columns are supported by an electrically grounded base.
 5. An electric switch as defined in claim 4 wherein the distance between said spherical electrodes when the switch is in its disengaged position is substantially shorter than the length of said insulator columns and the breakdown voltage for flashover is greater between said first and second electrodes than it is from said electrodes to said grounded base across the respective insulator column lengths.
 6. A high-voltage disconnect switch for ratings of 1,000 kv. and above comprising: first and second fixed spaced-apart electrodes having air only therebetween operative to produce a substantially uniform electrostatic field in air between facing surfaces thereof when in a disengaged switch position, each such electrode having an opening in its respective facing surface; and a retractable switchblade arranged to slidably move within at least one of said two electrodes in a direction alternatively towards and away from said other electrode by drive means positioned within at least said one electrode to connect and disconnect said electrodes, respectively, by contact means positioned within said other electrode; the longitudinal dimension of said retractable switchblade being greater than the spacing between said electrodes.
 7. A high-voltage electric disconnect switch for ratings of 1, 000 kv. and above comprising: first and second fixed spaced-apart electrodes having only air therebetween operative to produce a substantially uniform electrostatic field in the air between facing surfaces thereof when in a disengaged switch position, each such electrode having an opening in its respective facing surface; a retractable switchblade; and means operative to move said switchblade between said electrodes and through said surface openings to contact said electrodes when in an engaged switch position and to withdraw said retractable switchblade within one of said two electrodes to break said contact when in said disengaged position; the longitudinal dimension of said switchblade being greater than the spacing between said electrode surfaces but less then the dimension of said one of said spaced-apart electrodes within which said switchblade is withdrawn, said electrode dimension being measured along an axis which is substantially parallel to the plane of switchblade movement.
 8. An electric switch as defined in claim 7 wherein said first and second spaced-apart electrodes are operative to produce a sphere gap condition therebetween when in said disengaged switch position.
 9. An electric switch as defined in claim 8 wherein said spaced-apart electrodes comprise a pair of spherical electrodes and wherein the longitudinal dimension of said switchblade is greater than the spacing between the facing surfaces of said spherical electrodes but less then the diameter of that one of said spherical electrodes within which said switchblade is withdrawn. 